High-pressure structural study of the scheelite tungstates CaWO4 and SrWO4

TL;DR

This study investigates the high-pressure structural behavior of CaWO4 and SrWO4 tungstates using X-ray techniques and calculations, revealing phase transitions and proposing a new structure with implications for related materials.

Contribution

It provides experimental and theoretical insights into phase transitions of CaWO4 and SrWO4 under high pressure, including a new predicted phase and a relationship for bulk modulus estimation.

Findings

Both tungstates undergo scheelite-to-fergusonite transition around 10 GPa.

A second phase transition to a Cmca structure is predicted.

A linear correlation between charge density and bulk modulus is discussed.

Abstract

Angle-dispersive x-ray diffraction (ADXRD) and x-ray absorption near edge structure (XANES) measurements have been performed in the AWO4 tungstates CaWO4 and SrWO4 under high pressure up to approximately 20 GPa. Similar phase transitions and phase transition pressures have been observed for both tungstates using the two techniques in the studied pressure range. Both materials are found to undergo a pressure-induced scheelite-to-fergusonite phase transition under sufficiently hydrostatic conditions. Our results are compared to those found previously in the literature and supported by ab initio total energy calculations. From the total energy calculations we have also predicted a second phase transition from the fergusonite structure to a new structure identified as Cmca. Finally, a linear relationship between the charge density in the AO8 polyhedra of ABO4 scheelite-related structures and the bulk modulus is discussed and used to predict the bulk modulus of other materials, like zircon.